ded/cpp-httplib @ 1f34c541b0aa1b9be32e52e4d30276f8199d62d7

title: "HTTPS Server"

order: 7

In the previous chapter, you used an HTTPS client. Now let's set up your own HTTPS server. Just swap httplib::Server from Chapter 3 with httplib::SSLServer.

A TLS server needs a server certificate and a private key, though. Let's get those ready first.

Creating a Self-Signed Certificate

For development and testing, a self-signed certificate works just fine. You can generate one quickly with an OpenSSL command.

openssl req -x509 -noenc -keyout key.pem -out cert.pem -subj /CN=localhost

This creates two files:

cert.pem — Server certificate
key.pem — Private key

A Minimal HTTPS Server

Once you have your certificate, let's write the server.

#define CPPHTTPLIB_OPENSSL_SUPPORT
#include "httplib.h"
#include <iostream>

int main() {
    httplib::SSLServer svr("cert.pem", "key.pem");

    svr.Get("/", [](const auto &, auto &res) {
        res.set_content("Hello, HTTPS!", "text/plain");
    });

    std::cout << "Listening on https://localhost:8443" << std::endl;
    svr.listen("0.0.0.0", 8443);
}

Just pass the certificate and private key paths to the httplib::SSLServer constructor. The routing API is exactly the same as httplib::Server from Chapter 3.

Compile and start it up.

Testing It Out

With the server running, try accessing it with curl. Since we're using a self-signed certificate, add the -k option to skip certificate verification.

curl -k https://localhost:8443/
# Hello, HTTPS!

If you open https://localhost:8443 in a browser, you'll see a "This connection is not secure" warning. That's expected with a self-signed certificate. Just proceed past it.

Connecting from a Client

Let's connect using httplib::Client from the previous chapter. There are two ways to connect to a server with a self-signed certificate.

Option 1: Disable Certificate Verification

This is the quick and easy approach for development.

#define CPPHTTPLIB_OPENSSL_SUPPORT
#include "httplib.h"
#include <iostream>

int main() {
    httplib::Client cli("https://localhost:8443");
    cli.enable_server_certificate_verification(false);

    auto res = cli.Get("/");
    if (res) {
        std::cout << res->body << std::endl;  // Hello, HTTPS!
    }
}

Option 2: Specify the Self-Signed Certificate as a CA Certificate

This is the safer approach. You tell the client to trust cert.pem as a CA certificate.

#define CPPHTTPLIB_OPENSSL_SUPPORT
#include "httplib.h"
#include <iostream>

int main() {
    httplib::Client cli("https://localhost:8443");
    cli.set_ca_cert_path("cert.pem");

    auto res = cli.Get("/");
    if (res) {
        std::cout << res->body << std::endl;  // Hello, HTTPS!
    }
}

This way, only connections to the server with that specific certificate are allowed, preventing impersonation. Use this approach whenever possible, even in test environments.

Comparing Server and SSLServer

The httplib::Server API you learned in Chapter 3 works exactly the same with httplib::SSLServer. The only difference is the constructor.

| | httplib::Server | httplib::SSLServer | | -- | ------------------ | -------------------- | | Constructor | No arguments | Certificate and private key paths | | Protocol | HTTP | HTTPS | | Port (convention) | 8080 | 8443 | | Routing | Same | Same |

To switch an HTTP server to HTTPS, just change the constructor.

Next Steps

Your HTTPS server is up and running. You now have the basics of both HTTP/HTTPS clients and servers covered.

Next, let's look at the WebSocket support that was recently added to cpp-httplib.

Next: WebSocket

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